diff --git a/web/src/app.css b/web/src/app.css
index 1a18c361..52c52004 100644
--- a/web/src/app.css
+++ b/web/src/app.css
@@ -727,8 +727,11 @@ dialog.attachment-image-lightbox .attachment-image-lightbox-close:hover {
 	/* Modals / dialogs / tooltips. Most KeyboardShortcuts-style overlays
 	   carry role="dialog" on the backdrop. The shared Modal primitive uses a
 	   native <dialog> (implicit dialog role, no literal role attribute), so it
-	   is covered by the `dialog[open]` selector above. */
-	[role="dialog"],
+	   is covered by the `dialog[open]` selector above.
+	   `:not(.item-pane)` keeps the detail pane printable: on mobile the pane
+	   carries role="dialog" (TASK-2131) but IS the content being printed, not a
+	   transient overlay to strip. */
+	[role="dialog"]:not(.item-pane),
 	[role="tooltip"],
 	[role="menu"] {
 		display: none !important;
diff --git a/web/src/lib/collections/paneFocus.svelte.test.ts b/web/src/lib/collections/paneFocus.svelte.test.ts
index 96a9d14e..1fd1288b 100644
--- a/web/src/lib/collections/paneFocus.svelte.test.ts
+++ b/web/src/lib/collections/paneFocus.svelte.test.ts
@@ -4,6 +4,7 @@ import {
 	paneFocusables,
 	nextTrapTarget,
 	resolvePaneReturnTarget,
+	inExemptSurface,
 } from './paneFocus';
 
 // jsdom has no layout engine, so `offsetParent` / `getClientRects` can't gate
@@ -64,6 +65,47 @@ describe('paneFocusables', () => {
 	});
 });
 
+describe('inExemptSurface', () => {
+	it('does NOT treat the pane region itself as exempt (TASK-2131)', () => {
+		// The mobile overlay carries role="dialog"; an in-pane control must not be
+		// seen as an exempt foreign surface (that killed the mobile Tab trap and
+		// confused the focus-follows classifier). Excluded via `:not(.item-pane)`.
+		const root = mount(`
+			<aside class="item-pane" role="dialog" aria-modal="true">
+				<button id="in-pane">edit</button>
+			</aside>
+		`);
+		expect(inExemptSurface(root.querySelector('#in-pane'))).toBe(false);
+	});
+
+	it('treats a nested dialog/menu opened FROM the pane as exempt', () => {
+		// A real overlay (e.g. a BottomSheet or field-select menu) that portals in
+		// while the pane is open still owns its own focus/keyboard.
+		const root = mount(`
+			<aside class="item-pane" role="dialog">
+				<div role="menu"><button id="menu-item">move to…</button></div>
+			</aside>
+			<div role="dialog" id="sheet"><button id="sheet-btn">confirm</button></div>
+		`);
+		expect(inExemptSurface(root.querySelector('#menu-item'))).toBe(true);
+		expect(inExemptSurface(root.querySelector('#sheet-btn'))).toBe(true);
+	});
+
+	it('treats a native <dialog> and standalone overlays as exempt; nothing else', () => {
+		const root = mount(`
+			<dialog open><button id="native">ok</button></dialog>
+			<div role="listbox"><div id="opt">option</div></div>
+			<div class="block-context-menu"><button id="ctx">turn into</button></div>
+			<button id="plain">plain</button>
+		`);
+		expect(inExemptSurface(root.querySelector('#native'))).toBe(true);
+		expect(inExemptSurface(root.querySelector('#opt'))).toBe(true);
+		expect(inExemptSurface(root.querySelector('#ctx'))).toBe(true);
+		expect(inExemptSurface(root.querySelector('#plain'))).toBe(false);
+		expect(inExemptSurface(null)).toBe(false);
+	});
+});
+
 describe('nextTrapTarget', () => {
 	function setup() {
 		const container = mount(`<a href="/1">1</a><a href="/2">2</a><a href="/3">3</a>`);
diff --git a/web/src/lib/collections/paneFocus.ts b/web/src/lib/collections/paneFocus.ts
index 7e0ebf15..f447169f 100644
--- a/web/src/lib/collections/paneFocus.ts
+++ b/web/src/lib/collections/paneFocus.ts
@@ -57,9 +57,16 @@ export function paneFocusables(
  *     must not read a focus / pointerdown on them as a master↔pane switch.
  * ONE definition shared by both call sites (PaneHost's mobile trap + the host
  * route's activePane classifier) so the two can't drift.
+ *
+ * `[role="dialog"]:not(.item-pane)` EXCLUDES the pane region itself (TASK-2131):
+ * the mobile overlay now carries `role="dialog"` (a true modal), but it is the
+ * region these consumers operate ON, not a foreign overlay to defer to — without
+ * the `:not`, `closest()` from any in-pane element would match the pane and
+ * wrongly mark the whole pane exempt (killing the mobile Tab trap and confusing
+ * the classifier). A genuinely nested dialog opened FROM the pane still matches.
  */
 export const PANE_EXEMPT_SURFACE_SELECTOR =
-	'dialog, [role="dialog"], [role="menu"], [role="listbox"], .block-context-menu';
+	'dialog, [role="dialog"]:not(.item-pane), [role="menu"], [role="listbox"], .block-context-menu';
 
 /** True when `el` (or an ancestor) is one of the {@link PANE_EXEMPT_SURFACE_SELECTOR} overlays. */
 export function inExemptSurface(el: Element | null | undefined): boolean {
diff --git a/web/src/lib/components/collections/PaneHost.svelte b/web/src/lib/components/collections/PaneHost.svelte
index f5eb6c72..d7849e4f 100644
--- a/web/src/lib/components/collections/PaneHost.svelte
+++ b/web/src/lib/components/collections/PaneHost.svelte
@@ -26,6 +26,7 @@
 	import { onDestroy, untrack } from 'svelte';
 	import ItemDetail from '$lib/components/items/ItemDetail.svelte';
 	import { viewport } from '$lib/stores/breakpoint.svelte';
+	import { paneOverlay } from '$lib/stores/paneOverlay.svelte';
 	import { paneFocusables, nextTrapTarget, inExemptSurface } from '$lib/collections/paneFocus';
 	import type { PaneTarget } from '$lib/types';
 
@@ -330,10 +331,11 @@
 	//    can't see these).
 	// Both DEFER to a native modal <dialog> (Share / Edit Collection / the
 	// Open-Children confirm — `Modal.svelte` uses `showModal()`), which renders
-	// in the top layer above the overlay and owns its own focus cycle. `<aside>`
-	// isn't a dialog, so this never exempts the pane itself; role="dialog" sheets
-	// (BottomSheet) sit BELOW the pane and stay behind it, so focus belongs on
-	// the pane, not them.
+	// in the top layer above the overlay and owns its own focus cycle. The pane
+	// itself now carries `role="dialog"` on mobile (TASK-2131), so the exempt
+	// selector excludes it via `:not(.item-pane)` — the trap must NOT treat the
+	// region it's guarding as an exempt surface; role="dialog" sheets (BottomSheet)
+	// sit BELOW the pane and stay behind it, so focus belongs on the pane, not them.
 	$effect(() => {
 		if (!browser) return;
 		if (!paneEl || !viewport.isMobile) return;
@@ -377,6 +379,25 @@
 		};
 	});
 
+	// App-shell isolation for the mobile modal (PLAN-2105 / TASK-2131). The
+	// focus trap + `aria-modal` above keep KEYBOARD focus in the overlay, but a
+	// JS trap can't constrain a screen-reader virtual cursor and `aria-modal`
+	// alone is unevenly honored — so the app-shell chrome the layout renders
+	// (`MobileContextBar` + `BottomNav`) must physically leave the a11y tree
+	// while the overlay is up. That chrome lives in `+layout.svelte`, ABOVE this
+	// host, so we can't `inert` it by prop; instead register the active overlay
+	// in a shared store the layout reads (the list column, in-DOM here, is
+	// already inerted directly). Gated on the SAME condition as the trap
+	// (`viewport.isMobile && openItemRef`); the cleanup releases the ref on
+	// unmount and on any dep change (breakpoint crossing, `openItemRef`
+	// clearing), so desktop and closed states never inert the chrome.
+	$effect(() => {
+		if (!browser) return;
+		if (!openItemRef || !viewport.isMobile) return;
+		paneOverlay.enter();
+		return () => paneOverlay.leave();
+	});
+
 	// Desktop focusin backstop (PLAN-2154 Architecture C / R1, TASK-2162) — the
 	// NARROWED desktop mirror of the mobile trap's focusin catch-all above.
 	// `focusPaneRegion` (fired synchronously at each hop) is the primary R1
@@ -545,14 +566,21 @@
 	first paint when there's no stored value.
 -->
 <!--
-	`aside` gives the pane complementary-landmark semantics; `aria-label`
-	names it so a screen reader announces the region on entry (TASK-2122).
-	`tabindex="-1"` makes it a programmatic focus target (not a Tab stop):
-	Tab from the list moves focus here, and the mobile overlay moves focus
-	here on open (then traps it). Desktop keeps focus on the list so j/k
-	navigation is uninterrupted. Focus-in (mobile), the Tab bridge, ESC
-	return-to-list, and the mobile focus trap are wired in the effects +
-	the host's keydown handler.
+	`aria-label` names the pane so a screen reader announces the region on
+	entry (TASK-2122). `tabindex="-1"` makes it a programmatic focus target
+	(not a Tab stop): Tab from the list moves focus here, and the mobile
+	overlay moves focus here on open (then traps it). Desktop keeps focus on
+	the list so j/k navigation is uninterrupted. Focus-in (mobile), the Tab
+	bridge, ESC return-to-list, and the mobile focus trap are wired in the
+	effects + the host's keydown handler.
+
+	Role is viewport-dependent (PLAN-2105 / TASK-2131). On the DESKTOP split
+	the pane is a non-modal companion to the list, so it stays a bare `<aside>`
+	(implicit `complementary` landmark) with no `aria-modal`. On MOBILE it's a
+	full-screen overlay covering everything, so it becomes a `role="dialog"`
+	`aria-modal="true"` modal — paired with the app-shell chrome being inerted
+	(the overlay effect above) and the mobile focus trap for a complete modal.
+	`aria-label` supplies the required accessible name in the dialog case.
 -->
 <!-- svelte-ignore a11y_no_noninteractive_tabindex -->
 <aside
@@ -560,6 +588,8 @@
 	bind:this={paneEl}
 	tabindex="-1"
 	aria-label="Item detail"
+	role={viewport.isMobile ? 'dialog' : undefined}
+	aria-modal={viewport.isMobile ? 'true' : undefined}
 	style={paneWidth != null ? `--pane-width: ${paneWidth}px` : undefined}
 >
 	{#if paneMintForRoute}
diff --git a/web/src/lib/stores/paneOverlay.svelte.test.ts b/web/src/lib/stores/paneOverlay.svelte.test.ts
new file mode 100644
index 00000000..32a34324
--- /dev/null
+++ b/web/src/lib/stores/paneOverlay.svelte.test.ts
@@ -0,0 +1,51 @@
+// Runs in the jsdom vitest project (filename ends `.svelte.test.ts`), which
+// compiles the `.svelte.ts` rune module. `paneOverlay` is a ref-counted signal
+// (TASK-2131): PaneHost calls enter()/leave() per active mobile overlay and the
+// workspace layout reads `mobileOverlayActive` to inert the app-shell chrome.
+// The module holds process-wide `$state`, so each test re-imports a fresh copy.
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+
+beforeEach(() => {
+	// Fresh module (and its process-wide $state count) per test.
+	vi.resetModules();
+});
+
+describe('paneOverlay', () => {
+	it('starts inactive', async () => {
+		const { paneOverlay } = await import('./paneOverlay.svelte');
+		expect(paneOverlay.mobileOverlayActive).toBe(false);
+	});
+
+	it('is active after a single enter() and inactive after the matching leave()', async () => {
+		const { paneOverlay } = await import('./paneOverlay.svelte');
+		paneOverlay.enter();
+		expect(paneOverlay.mobileOverlayActive).toBe(true);
+		paneOverlay.leave();
+		expect(paneOverlay.mobileOverlayActive).toBe(false);
+	});
+
+	it('stays active while overlapping overlays are open (ref-counted)', async () => {
+		// Models a route change where the incoming PaneHost enters before the
+		// outgoing one's effect cleanup leaves — the signal must not flicker off.
+		const { paneOverlay } = await import('./paneOverlay.svelte');
+		paneOverlay.enter(); // outgoing host
+		paneOverlay.enter(); // incoming host mounts before...
+		expect(paneOverlay.mobileOverlayActive).toBe(true);
+		paneOverlay.leave(); // ...outgoing host's cleanup runs
+		expect(paneOverlay.mobileOverlayActive).toBe(true);
+		paneOverlay.leave();
+		expect(paneOverlay.mobileOverlayActive).toBe(false);
+	});
+
+	it('never goes negative on an unmatched leave()', async () => {
+		// A defensive floor: a stray leave() (double-cleanup) can't drive the
+		// count below zero and wedge a later enter() into staying inactive.
+		const { paneOverlay } = await import('./paneOverlay.svelte');
+		paneOverlay.leave();
+		expect(paneOverlay.mobileOverlayActive).toBe(false);
+		paneOverlay.enter();
+		expect(paneOverlay.mobileOverlayActive).toBe(true);
+		paneOverlay.leave();
+		expect(paneOverlay.mobileOverlayActive).toBe(false);
+	});
+});
diff --git a/web/src/lib/stores/paneOverlay.svelte.ts b/web/src/lib/stores/paneOverlay.svelte.ts
new file mode 100644
index 00000000..472cb5d6
--- /dev/null
+++ b/web/src/lib/stores/paneOverlay.svelte.ts
@@ -0,0 +1,35 @@
+// Ref-counted signal for "a mobile full-screen detail-pane overlay is active"
+// (PLAN-2105 / TASK-2131). At ≤768px the detail pane (PaneHost's `.item-pane`)
+// restyles to a full-viewport modal overlay covering the app-shell chrome.
+// While it's up, the workspace layout marks the chrome siblings it renders —
+// `MobileContextBar` + `BottomNav` — `inert` so they leave the focus order AND
+// the screen-reader tree. A JS focus trap plus `aria-modal="true"` on the pane
+// can't fully constrain an SR virtual cursor, so the background chrome must
+// physically drop out of the a11y tree — the same treatment the collection
+// host already gives its list column (`inert={viewport.isMobile && openItemRef}`).
+// The chrome lives in `+layout.svelte`, ABOVE the pane host, so the host can't
+// reach it by prop; it hoists the fact into this store instead.
+//
+// Ref-counted rather than a bare boolean so a brief overlap of two mounted
+// overlays — e.g. a client route change from the collection host to the
+// full-page item host where the incoming PaneHost's effect runs before the
+// outgoing one's cleanup — can't clear the signal early. PaneHost is the only
+// writer (one `enter`/`leave` per active overlay via an `$effect`); the layout
+// is the only reader. This one-way split satisfies CONVE-1688 — a store must
+// never read state it also writes.
+let overlayCount = $state(0);
+
+export const paneOverlay = {
+	/** True while ≥1 mobile detail-pane overlay is active. Read by the workspace layout. */
+	get mobileOverlayActive() {
+		return overlayCount > 0;
+	},
+	/** Register a newly-active mobile overlay. Pair every call with `leave()`. */
+	enter() {
+		overlayCount += 1;
+	},
+	/** Release a mobile overlay that stopped being active (unmount / breakpoint / close). */
+	leave() {
+		overlayCount = Math.max(0, overlayCount - 1);
+	},
+};
diff --git a/web/src/routes/[username]/[workspace]/+layout.svelte b/web/src/routes/[username]/[workspace]/+layout.svelte
index cce7bd87..fa32a7fb 100644
--- a/web/src/routes/[username]/[workspace]/+layout.svelte
+++ b/web/src/routes/[username]/[workspace]/+layout.svelte
@@ -12,6 +12,7 @@
 	import { titleStore } from '$lib/stores/title.svelte';
 	import { authStore } from '$lib/stores/auth.svelte';
 	import { registerWorkspaceTools, type WebMcpHandle } from '$lib/webmcp/register';
+	import { paneOverlay } from '$lib/stores/paneOverlay.svelte';
 	import ConnectBanner from '$lib/components/ConnectBanner.svelte';
 	import VerifyEmailBanner from '$lib/components/VerifyEmailBanner.svelte';
 	import BottomNav from '$lib/components/layout/BottomNav.svelte';
@@ -246,16 +247,34 @@
 	}
 </script>
 
-<VerifyEmailBanner />
+<!--
+	App-shell chrome (PLAN-2105 / TASK-2131). While a mobile detail-pane overlay
+	is up (`paneOverlay.mobileOverlayActive`, set by PaneHost) every app-shell
+	sibling the layout renders sits BEHIND the full-screen modal, so all of them
+	are marked `inert` — out of the focus order and the screen-reader tree.
+	`aria-modal` on the pane isn't reliably honored on its own, so the background
+	must physically leave the a11y tree; that has to cover the banners
+	(VerifyEmailBanner's Resend, ConnectBanner's action) as well as the context
+	bar / bottom nav, or their controls stay reachable behind the modal. Only
+	`{@render children()}` — which contains the pane itself — is left interactive.
+	`display: contents` wrappers carry the `inert` (which cascades to descendants)
+	without adding a box, so the fixed chrome renders exactly as before. Off mobile
+	/ pane closed the signal is false and the attribute is absent — no desktop change.
+-->
+<div style="display: contents" inert={paneOverlay.mobileOverlayActive}>
+	<VerifyEmailBanner />
 
-<ConnectBanner
-	{wsSlug}
-	serverUrl={typeof window !== 'undefined' ? window.location.origin : ''}
-	workspaceName={workspaceStore.current?.name ?? ''}
-/>
+	<ConnectBanner
+		{wsSlug}
+		serverUrl={typeof window !== 'undefined' ? window.location.origin : ''}
+		workspaceName={workspaceStore.current?.name ?? ''}
+	/>
 
-<MobileContextBar />
+	<MobileContextBar />
+</div>
 
 {@render children()}
 
-<BottomNav />
+<div style="display: contents" inert={paneOverlay.mobileOverlayActive}>
+	<BottomNav />
+</div>
diff --git a/web/src/routes/[username]/[workspace]/[collection]/+page.svelte b/web/src/routes/[username]/[workspace]/[collection]/+page.svelte
index 11833e55..55c76dbb 100644
--- a/web/src/routes/[username]/[workspace]/[collection]/+page.svelte
+++ b/web/src/routes/[username]/[workspace]/[collection]/+page.svelte
@@ -2189,9 +2189,12 @@
 			// (not bare `dialog`) because `Modal.svelte`'s native <dialog> is
 			// ALWAYS mounted and toggled via `showModal()`/`close()` — an
 			// existence check without `[open]` would false-positive on every page
-			// that merely HAS a Modal instance, open or not. The pane (<aside>)
-			// and graph drawer aren't dialogs, so this never blocks the chain.
-			if (document.querySelector('dialog[open], [role="dialog"]')) return;
+			// that merely HAS a Modal instance, open or not. The pane itself now
+			// carries `role="dialog"` on the mobile overlay (TASK-2131), so it is
+			// EXCLUDED via `:not(.item-pane)` — its ESC is owned by its own escape-
+			// stack handler, and counting it here would swallow ESC-to-close / pop.
+			// The graph drawer isn't a dialog, so the chain is otherwise unblocked.
+			if (document.querySelector('dialog[open], [role="dialog"]:not(.item-pane)')) return;
 			// A HELD key fires many auto-repeat keydowns (`e.repeat === true`).
 			// Consumed here, BEFORE any layer-close/pop decision, so a hold can
 			// never cascade through the chain — only the initial physical press
diff --git a/web/src/routes/[username]/[workspace]/[collection]/[slug]/+page.svelte b/web/src/routes/[username]/[workspace]/[collection]/[slug]/+page.svelte
index 848ab6a4..8f750b1e 100644
--- a/web/src/routes/[username]/[workspace]/[collection]/[slug]/+page.svelte
+++ b/web/src/routes/[username]/[workspace]/[collection]/[slug]/+page.svelte
@@ -430,8 +430,11 @@
 		const target = e.target as HTMLElement | null;
 		// Text-editing targets own ESC locally — don't hijack into a layer-close.
 		if (isTextEntryTarget(target)) return;
-		// A native <dialog> / role="dialog" sheet owns its own ESC.
-		if (document.querySelector('dialog[open], [role="dialog"]')) return;
+		// A native <dialog> / role="dialog" sheet owns its own ESC. The pane's own
+		// mobile overlay is `role="dialog"` too (TASK-2131) but is EXCLUDED via
+		// `:not(.item-pane)` — it's the layer this ESC is meant to close, handled
+		// through the shared escape stack, not a foreign modal to defer to.
+		if (document.querySelector('dialog[open], [role="dialog"]:not(.item-pane)')) return;
 		// A HELD key auto-repeats; only the initial physical press acts.
 		if (e.repeat) {
 			e.preventDefault();